Long-Term Vibration Monitoring of the I-35W St. Anthony Falls Bridge A THESIS SUBMITTED TO

100 Pages·2017·2.59 MB·English

by  Karl O Gaebler

Long-Term Vibration Monitoring of the I-35W St. Anthony Falls Bridge

A THESIS
SUBMITTED TO THE FACULTY OF
UNIVERSITY OF MINNESOTA
BY

Karl O. Gaebler

IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
MASTER OF SCIENCE

Dr. Lauren E. Linderman, Dr. Carol K. Shield

May, 2017
© Karl O. Gaebler 2017
ALL RIGHTS RESERVED
Acknowledgements

I would like to acknowledge the many people who have contributed their
time and support to this project, particularly my advisers Lauren Linderman and
Carol Shield. I would also like to acknowledge the support of the Minnesota
Department of Transportation. Numerical computations were performed using
resources provided by the University of Minnesota Supercomputing Institute.

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Dedication

I would like to dedicate this work to my family:

To my brother and sister, who always motivate me to be the best I can be
through their accomplishments as well as their unending support of my own.

To my parents who have given me nothing but unconditional love and
support, and have blindly trusted me in any endeavor I pursue. Thanks to you, I
have come a long way from Owl Moon.
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Abstract

Vibration based structural health monitoring has become more common in
recent years as the required data acquisition and analysis systems become more
affordable to deploy. It has been proposed that by monitoring changes in the
dynamic signature of a structure, primarily the natural frequency, one can detect
damage. This approach to damage detection is made difficult by the fact that
environmental factors, such as temperature, have been shown to cause variation
in the dynamic signature in a structure, effectively masking those changes due to
damage. Another parameter, such as displacement estimates, may be better
suited for damage detection, however and effective and accurate routine for such
estimates is required. A monitoring system on the I-35W St. Anthony Falls
Bridge, which crosses the Mississippi River in Minneapolis, MN, has been
collecting vibration and temperature data since the structures opening in 2008.
This provides a uniquely large data set, in a climate that sees extreme variation
in temperature, to test the relationship between the dynamic signature of a
concrete structure and temperature. A system identification routine utilizing
NExT-ERA/DC is proposed to effectively analyze this large data set, and the
relationship between structural temperature and natural frequency is investigated,
and a displacement estimation technique is proposed.
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Table of Contents

List of Tables .................................................................................................. vi
List of Figures................................................................................................ vii
1. Introduction ....................................................................................... 1
2. Literature Review .............................................................................. 3
3. Data Acquisition and Processing .................................................... 12
3.1. Bridge Description and Instrumentation ............................... 13
3.2. Signal Processing ................................................................. 15
3.2.1. NExT-ERA/DC .................................................................. 16
3.2.2. Modal Order ..................................................................... 17
3.2.3. Number of Data Points and Windowing ............................ 17
3.2.4. Reference Channel Selection ........................................... 18
3.2.5. CMI ................................................................................... 20
3.3. Mode Sorting ........................................................................ 21
3.4. Signal Detection ................................................................... 22
4. System Identification Results .......................................................... 27
4.1. Identified Modal Parameters................................................. 27
4.2. Temperature Effects ............................................................. 29
4.2.1. Seasonal Effects............................................................... 29
4.2.2. Structural Temperature ..................................................... 30
4.3. Temperature Gradient Effects .............................................. 32
5. Displacement Estimation ................................................................ 35
5.1. Kalman Filter ........................................................................ 35
5.2. Proposed Method ................................................................. 37
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5.3. Single Story Results ............................................................. 40
5.4. I-35W ABAQUS Model Results ............................................ 41
6. Conclusion ...................................................................................... 45
Tables ............................................................................................. 49
Figures ................................................................................................. 53
References ................................................................................................. 74
Appendix A – Accelerometer Outages ......................................................... 80
Appendix B – NExT-ERA/DC ....................................................................... 81
Appendix C – CMI ........................................................................................ 86
Appendix D – Kalman Filter ......................................................................... 89

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List of Tables
Table 1: Success rate of NExT-ERA/DC with varying reference channel selection
........................................................................................................................... 49
Table 2: Assumed Displacement Vectors ........................................................... 49
Table 3: Success rate as a function of Peak Signal and RMS ............................ 50
Table 4: Identified Natural Frequencies and Damping ........................................ 50
Table 5: System Identification Parameters; Signal Detection Investigation ........ 51
Table 6: Name and location of thermistors utilized in temperature calculations . 51
Table 7: Output-Only Kalman filter performance ................................................ 52

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List of Figures
Figure 1: Elevation looking west of the new I-35W St. Anthony Falls Bridge ...... 53
Figure 2: Southbound Estimated Mode Shapes 1 Through 4 as Extracted
from F.E.A. ............................................................................................... 54
Figure 4: Accelerometer Layout, Plan View ........................................................ 55
Figure 5: Reference Channel Location with respect to F.E.A. Mode Shape
Results ..................................................................................................... 56
Figure 6: Success Rate as a Function of Peak Acceleration Signal: Modes
1 & 4 ........................................................................................................ 57
Figure 7: Success Rate as a Function of Acceleration Signal RMS: Modes
1 & 4 ........................................................................................................ 57
Figure 8: Success Rate as a Function of Peak to RMS Ratio: Modes 1 & 4 ...... 57
Figure 9: Peak-to-RMS Ratio of Sample Vibration Signals ................................. 58
Figure 10: Identified mode Shape of the First Mode ........................................... 58
Figure 11: Identified mode Shape of the Second Mode ...................................... 59
Figure 12: Identified mode Shape of the Third Mode .......................................... 59
Figure 13: Identified mode Shape of the Fourth Mode ....................................... 60
Figure 14: Monthly Average Natural Frequency of the First Mode ..................... 60
Figure 15: Monthly Average Natural Frequency of the Second Mode ................ 61
Figure 16: Monthly Average Natural Frequency of the Third Mode .................... 61
Figure 17: Monthly Average Natural Frequency of the Fourth Mode .................. 61
Figure 18: Variation of the First Natural Frequency with Temperature ............... 62
Figure 19: Variation of the Second Natural Frequency with Temperature .......... 62
Figure 20: Variation of the Third Natural Frequency with Temperature .............. 63
Figure 21: Variation of the Fourth Natural Frequency with Temperature ............ 63
Figure 22: Variation in First Natural Frequency with Temperature ..................... 64
Figure 23: Variation in Second Natural Frequency with Temperature ................ 64
Figure 24: Variation in Third Natural Frequency with Temperature .................... 65
Figure 25: Variation in Fourth Natural Frequency with Temperature .................. 65
Figure 26: Effects of Spatial Gradient on the First Natural Frequency ................ 66
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Figure 27: Effects of Spatial Gradient on the Second Natural Frequency .......... 66
Figure 28: Effects of Spatial Gradient on the Third Natural Frequency .............. 67
Figure 29: Effects of Spatial Gradient on the Fourth Natural Frequency ............ 67
Figure 30: Effects of Temporal Gradient on the First Natural Frequency ........... 68
Figure 31: Effects of Temporal Gradient on the Second Natural Frequency ...... 68
Figure 32: Effects of Temporal Gradient on the Third Natural Frequency .......... 69
Figure 33: Effects of Temporal Gradient on the Fourth Natural Frequency ........ 69
Figure 34: SDOF Kalman Filter Experimental Setup .......................................... 70
Figure 35: Transfer Function – Curve Fit SDOF Model ...................................... 70
Figure 36: Transfer Function – Output-Only SDOF Model ................................. 71
Figure 37: Estimated Displacement of a SDOF System Using a Curve Fit
Model ....................................................................................................... 71
Figure 38: Estimated Displacement of a SDOF System Using an Output-
Only Model ............................................................................................... 72
Figure 39: 2D I-35W St. Anthony Falls Bridge F.E. Model .................................. 72
Figure 40: Finite Element Output and Estimated Displacements of the I-
35W Bridge .............................................................................................. 73
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